The present invention relates to a mounting process simulation system for carrying out simulations of a mounting process comprising a plurality of steps by using a computer and a method thereof, and more particularly, to a mounting process simulation system for sequentially simulating a plurality of steps and a method thereof.
Conventionally, as a method for determining the conditions of a mounting process for mounting various electronic components on a circuit board, a simulation was carried out using a CAE (Computer Aided Engineering) tool at each step, or production was carried out experimentally on conditions similar to actual mounting conditions. This kind of method for determining the conditions of the mounting process is carried out in reflow soldering processing, for example. The reflow soldering processing includes a solder printing step, a component placement step and a reflow step. At the solder printing step, on a circuit board on which predetermined circuit patterns are formed, solder is printed onto the electrode portions of the circuit patterns so as to be electrically connected to components serving as electronic components to be mounted on this circuit board. At the component placement step, components to be mounted on the printed solder are placed. At the reflow step, the printed solder is heated and melted, whereby the electrodes of the components are electrically connected to the circuit patterns, and the components are firmly fixed at desired positions on the circuit board. These solder printing step, component placement step and reflow step are carried out sequentially in general reflow soldering processing.
To evaluate this kind of mounting process, simulation systems for analyzing and evaluating failure phenomena of mounted products have been proposed. For example, in Japanese Unexamined Patent Publication No. 2002-232131, a thermal analysis apparatus and a heating condition calculation apparatus are described wherein in order to determine heating conditions to be given to a heating apparatus in reflow soldering processing, heating conditions are derived by introducing the geometric factors of substances to be heated.
In the case when process conditions are determined for mounted products, it is necessary to carry out a simulation at each step of the mounting process. A plurality of simulations were required, for example, the analysis of a soldering state at a solder printing step; the analysis of a component placement state at a component placement step; and the analysis of behavior, the positional analysis of electronic components with respect to a circuit board, the reliability evaluation of the circuit board, etc. at the final step. In other words, in the case when n (n: any natural number) steps that were required to be simulated in the mounting process were present, users had to carry out at least n simulations.
In the conventional simulation system, when condition parameters best suited for the mounting step were set, such a method as typified by Taguchi Method was used to reduce the time required for a simulation. Taguchi Method is a method wherein predetermined initial parameters are prepared in advance and a simulation is carried out on the basis of the initial parameters. In Taguchi Method, an approximate model is created by using the results obtained by the simulation, and optimum parameters are searched for, whereby condition parameters are determined.
However, in the case when a simulation is carried out by using Taguchi Method, the user is required to determine appropriate initial parameters in advance. Furthermore, after the simulation, the user must determine condition parameters depending on calculated data.
In this kind of method wherein a simulation is carried out by using initial parameters determined in advance and an approximate model is created, since the sample number of initial parameters to be determined in advance is unknown, numerous initial parameters are determined; as a result, too many simulations are required to be carried out. In addition, since the user cannot accurately judge whether the obtained analysis results are optimal or not, there is a possibility that the user might select improper condition parameters.
Furthermore, for the evaluation of the entire mounting process, it was necessary to evaluate the analysis results of a plurality of simulations at the same time. For example, for the comprehensive evaluation of the performance of the entire process using the respective analysis results of the solder printing step, the component placement step and the reflow step in the mounting process, the user himself had to make comprehensive judgments on the basis of the results of the plurality of simulations.